1. Field of the Invention
This invention relates to a photographic color coupler and, more particularly, to a novel 2-equivalent cyan coupler, color photographic light-sensitive material containing that coupler, and image-forming process using the couplers.
2. Description of the Prior Art
It is well known that when an imagewise exposed silver halide photographic light-sensitive material is subjected to color development processing, an oxidation product of the aromatic primary amine developing agent reacts with a dye-forming coupler to form a color image.
Usually, a color-reproducing process based on subtractive color photography is relied upon forming cyan, magenta, and yellow color images, the colors of which are in complementary relation with red, green, and blue, respectively. For example, phenolic derivatives or naphtholic derivatives used as couplers for forming cyan color images.
In color photography, color-forming couplers are added to a developer or incorporated in a light-sensitive photographic emulsion layer or other color image-forming layer and, when reacted with an oxidation product of a color-developing agent formed upon development, they form non-diffusing dyes. The reaction between the coupler and the color-developing agent proceeds at the active site of the coupler. Couplers having a hydrogen atom at this active site are 4-equivalent couplers which theoretically require 4 mols of silver halide with a developing center (exposed silver halide) as an oxidizing agent for forming 1 mol of a dye. On the other hand, couplers having at the active site a group capable of being eliminated as an anion are 2-equivalent couplers which require only two mols of silver halide with a developing center and, therefore, they generally permit a reduction in the amount of silver halide incorporated in a light-sensitive layer and in the thickness of the film, thus enabling one to shorten the time for processing light-sensitive materials and improving sharpness of color images to be formed. As such eliminatable or coupling-off group, U.S. Pat. No. 3,737,316 describes a sulfonamido group, U.S. Pat. No. 3,749,735 describes an imido group, U.S. Pat. No. 3,622,328 describes a sulfonyl group, U.S. Pat. No. 3,476,563 describes an aryloxy group, U.S. Pat. No. 3,311,476 describes an acyloxy group, and U.S. Pat. No. 3,214,437 describes a thiocyano group.
Further, U.S. Pat. No. 4,032,345 describes an isocyanato group, U.S. Pat. No. 4,046,573 describes a sulfonyloxy group, Japanese Patent Application (OPI) No. 51939/77 (The term "OPI" as used herein refers to a "published unexamined Japanese patent application") describes a thiocarbonyloxy group, Japanese Patent Application (OPI) Nos. 39126/78 and 39745/78 describe an aralkenylcarbonyloxy group, Japanese Patent Application (OPI) No. 45524/78 describes an S-substituted monothiocarbonyloxy group, Japanese Patent Application (OPI) No. 47827/78 describes a propioloyloxy group, U.S. Pat. No. 4,072,525 describes a group of ##STR1## and U.S. Pat. No. 3,227,551, Japanese Patent Application (OPI) Nos. 120334/75, 18315/77, 90932/77, 52423/78 and 99938/78 describe substituted alkoxy groups.
Proper selection of such eliminatable groups, for example, selection of a group having a diffusible dye moiety, permits the use of the couplers in a diffusion transfer process where images of diffusible dyes are formed in an image-receiving layer. Such couplers are called diffusible dye-releasing (DDR) couplers and are described in, for example, U.S. Pat. Nos. 3,227,550, U.S. Pat. No. 4,052,212 3,765,886, U.S. Defensive Publication No. T 900,029, British Pat. No. 1,330,524, etc. Some colored 2-equivalent couplers have the masking effect for color correction of a dye image, and such couplers are called color correction couplers described in, for example, Japanese Patent Application (OPI) No. 26034/76.
2-Equivalent couplers from which a development inhibiting product is eliminated are so-called development inhibitor-releasing couplers, which inhibit development in proportion to the amount of silver deposit, thus contributing to reduction in image-forming particle size, adjustment of gradation, and improvement of color reproduction. In addition, they can be used in a diffusion transfer process utilizing their action on an adjacent layer. These couplers are described in U.S. Pat. No. 3,227,554, Japanese Patent Application (OPI) No. 122335/74, and West German Patent Application (OLS) No. 2,414,006.
2-Equivalent couplers have important advantage over 4-equivalent couplers as described above and permit various applications, thus they are often used. However, many conventionally known 2-equivalent cyan-forming couplers have the defects of insufficient coupling reactivity, serious color fog, coating troubles due to poor dispersibility, poor storage stability, and poor color image stability.